1. Field of the Invention
The present invention relates to a method of manufacturing an organic electroluminescence (EL) display device and a manufacturing apparatus for carrying out the manufacturing method.
2. Description of the Related Art
A generally known display device having organic EL elements mounted thereon is a device in which pixels each having a single or multiple organic EL elements are arranged in a predetermined pattern. By those pixels, an emission region of the display device is two-dimensionally and finely divided. The organic EL elements included in the pixels are electronic elements which output, for example, any one of red light, green light, and blue light. A display device having organic EL elements mounted thereon obtains a full-color image by driving the organic EL elements for outputting desired colors at desired emission intensities.
By the way, in an organic EL element which is a component of a display device, an organic compound layer which is a component of the element is a thin film layer formed by forming a thin film made of an organic material by vapor deposition or the like. When the organic compound layer which is a component of the organic EL element of the display device is formed for each element, a fine patterning technology is necessary. In order to carry out patterning when an organic compound layer is vapor deposited, a fine metal mask the fineness of which is according to the fineness of the patterning is necessary. However, in a metal mask, a vapor deposited film which adheres when vapor deposition operation is performed may narrow an opening in the mask or stress may deform the opening in the mask. Therefore, it is necessary to clean the mask used after film formation for a fixed number of times, which is a disadvantageous factor from the viewpoint of manufacturing costs. Further, partly due to a limitation on the process accuracy of the mask, the pixel size has a limit of about 100 μm, which is disadvantageous to a finer size. Further, with regard to the substrate size, when a fine metal mask is increased in size, in order to secure the positional accuracy of the opening in the mask, it is necessary to enhance the stiffness of a frame of the mask. However, when the stiffness of the mask is enhanced, an increase in the weight of the mask itself is caused accordingly. Therefore, from the viewpoint of both processability and handling, it is difficult to manufacture large format display devices of the fourth and subsequent generations, and an optimum manufacturing process of a fine organic EL element and a display device having the organic EL element mounted thereon has not taken shape at present.
Under those circumstances, a method of manufacturing a display device having a fine organic EL element without using a metal mask is proposed. A method proposed in Japanese Patent No. 3813069 is a specific example of such a method. Here, the method proposed in Japanese Patent No. 3813069 is a method in which, after repeating three times for the respective colors a step of leaving an organic compound layer formed on an entire surface of a substrate selectively in a predetermined location by patterning using photolithography, a common electrode is formed. Another method which uses photolithography is proposed in Japanese Patent No. 4507759. Japanese Patent No. 4507759 discloses a method in which, through provision on an organic compound layer a water-soluble intermediate layer and carrying out photolithography, an organic compound layer is patterned.
However, when photolithography is used to pattern the organic compound layer which forms the organic EL element, there are some problems to be solved.
A first problem is that a constituent material of the organic compound layer is dissolved in an organic solvent used in a photo process. Here, the process proposed in Japanese Patent No. 3813069 enables an organic EL display device with higher definition compared with a case of a conventional method using a fine metal mask. However, there is a limitation that materials usable in the process proposed in Japanese Patent No. 3813069 are limited to materials which are insoluble in all of a photoresist solvent, a photoresist developer, and a photoresist remover. As a photoresist developer widely used in a manufacturing process of a silicon wafer or a substrate for a TFT, an organic solvent such as tetramethylammonium hydroxide is used. However, the constituent material of the organic compound layer is soluble in such an organic solvent, and thus, for example, a problem arises that, in a step of applying the resist, the constituent material of the organic compound layer and the resist are compatible with each other. Accordingly, for the sake of industrialization, for example, it is necessary to develop and prepare a dedicated photoresist material.
A second problem is that constituent materials of an electron injection layer and a cathode are required to be water-resistant. In an organic EL element manufactured by vacuum deposition, it is generally known to use an alkali metal compound as a constituent material of the electron injection layer for higher efficiency and lower voltage of the element. However, an alkali metal compound is a compound which is water-soluble or the characteristics of which are deteriorated by water. Therefore, in the process proposed in Japanese Patent No. 4507759, when an alkali metal compound is used as a constituent material of the electron injection layer, a problem arises that, when the organic compound layer is immersed in water or the like at a photolithography step, the electron injection layer is eluted. Even if the elution does not occur, a problem arises that, when the organic compound layer is immersed in water or the like, the electron injection characteristics of the electron injection layer are deteriorated.